The present invention relates to organic electroluminescent (EL) elements. More specifically, the invention relates to the use of a novel class of organic material for producing efficient organic EL devices.
Nowadays, with the fast development of science and technology, and their wide application to daily life, the requirement for good interfaces between users and machines is growing, such as information display for instruments, televisions, computers and so on. In order to gain ample, correct, concise, and high-speed information from the machine, the display elements have been widely studied.
While cathode ray tubes (CRTs) clearly dominate the market with their bright, saturated colors, they are also known to be heavy, power consuming, and bulky. For these reasons, flat panel displays are a highly attractive alternative for computers, television, wall-mounted large-screen video displays and a wide range of other applications.
An example of the flat panel display is the active-matrix liquid-crystal display, which is commercially available. Even though this technology is now widely used for laptop computer displays, in general it is not considered to be a widespread replacement for the CRT technology. The major shortcomings of the LCD-based display are that it is an inefficient color subtractive technology, requiring a power consumptive backlight. Also, it is relatively slow, and has a narrow viewing angle. One alternative to LCDs is based on conventional semiconductor light-emitting diode (LED) technology. However, the very high costs associated with the requirement of epitaxial multilayer structures make them an unlikely choice for use in low-cost displays in the near future.
A promising flat panel display free from the above-mentioned disadvantages is based on organic light-emitting diodes (OLEDs) that use an organic luminescent material for light emission. The organic luminescent materials are very attractive due to their versatility, richness in blue photoluminescence, and high photo-luminescent quantum yields.
The advantages of the OLED display are self-luminous, capable of high-speed response, and independent on viewing angle. These advantages will no doubt be successfully exploited, and the commercial use for organic EL devices will be realized in the near future.
To obtain high-performance OELDs with low carrier injection barriers, high electroluminescence (EL) efficiency and long lifetime, materials design and device configurations are two important factors. It is desirable that the OELD materials possess the following properties: good carrier transport properties, high photoluminescence (PL) quantum yield, and suitable ionization potential (IP) and/or electron affinity (EA). Thus, the synthesis of highly fluorescent and stable materials that can be utilized in OELDs is one of the most challenging works in this field.
Some polycyclic aromatic hydrocarbons (PAHs) have very high PL quantum yield and thus have been used in OELDs. Here are some reported examples using this kind of materials in OLEDs: 1) T. Sano, H. Fujii, Y. Nishio, Y. Hamada, H. Takahashi, K. Shibata, Syn. Met., 91, 27(1997); 2) J. Shi, C. W. Tang, C. H. Chen, U.S. Pat. No. 593,572 (1999); and 3) S. Tamura; T. Ishibashi, U.S. Pat. No. 5,858,564. The pure hydrocarbon conjugated structure of the compounds intrinsically determines their relatively high carrier transport abilities. Meanwhile, most of them are highly luminescent and relatively stable. It is thus considered that the PAHs compounds may have special importance for OELD applications.
In our invention, we have synthesized a new PAH compound, 1,9-perinaphthylene-10-1xe2x80x2-naphthylanthracene (pNNA), and utilized this compound in OLED fabrication.
The present invention provides an organic EL element comprising an anode, a cathode, and an organic light-emitting structure between the anode and the cathode. The luminescent material disclosed in this invention is utilized as a dopant in the organic light-emitting structure and has the following structure called pNNA or pNNA derivatives: 
Wherein:
R1, R2, R3, R4 are individual substituents or a group of substituents, and they may be identical or different. Each substituent is individually selected from the following groups consisting of:
H, alkyl (xe2x80x94R), halogen (xe2x80x94X), aryl (xe2x80x94Ar), alkenyl (RCHxe2x95x90CHxe2x80x94), allyl (CH2xe2x95x90CHCH2xe2x80x94), cyano (NCxe2x80x94), isocyano (CNxe2x80x94), amino (H2Nxe2x80x94), tertiary amino (R2Nxe2x80x94 or Ar1Ar2Nxe2x80x94), amide (RCONRxe2x80x94), nitro (N2Oxe2x80x94), acyl (RCOxe2x80x94), carboxyl (xe2x80x94CO2H), alkoxyl (ROxe2x80x94), alkylsulfonyl (RSO2xe2x80x94), hydroxy (HOxe2x80x94) and single or fused aromatic heterocyclic rings.
The electroluminescent element of the present invention emits light from pNNA or pNNA derivatives.
The first aspect of the present invention resides in an electroluminescent element having an anode, a cathode, and an organic layer structure between the two electrodes. The organic layer structure has a luminescent zone containing pNNA or one of its derivatives as a dopant. The second aspect of the present invention resides in a luminescent display formed of such electroluminescent elements.
The advantage of this invention is that because the pNNA or its derivatives are highly efficient with a narrow emission peak and a stable conjugated system, OLEDs utilizing these materials as a dopant exhibit high power efficiency, color purity and stability